WASHINGTON -- The U.S. Supreme Court on Tuesday began hearing an appeal of a Florida man arrested for possession of child pornography.

Michael Williams of Key Largo, Fla., was arrested in May 2004 after he allegedly took part in several exchanges with an undercover agent in an adult chat room on the Internet.

In 2003, Congress allowed agents to arrest anyone for advertising, promoting, presenting, distributing or soliciting material in a manner that is "intended to cause another to believe" the material is illegal child pornography, even if it's computer-generated and not real children.

John Feldmeier, a political science professor at Wright State University in Dayton, Ohio., who helped file a friend-of-the-court brief on behalf of the Free Speech Coalition, a trade association for the adult-entertainment industry, told the Christian Science Monitor the 2003 law was too vague and intrusive.

"It enters into an area that should be 100 percent off-limits to any form of government regulation," Feldmeier said. "Government should not be regulating the mind."